1. Field of the Invention
The present invention relates to a module battery of a sealed alkaline storage battery of a comparatively large capacity, a cell and a battery casing for configuring the battery.
2. Description of the Related Art
Sealed alkaline storage batteries, which typically include nickel-cadmium storage batteries and nickel-metal hydride storage batteries, are widely used as power supply sources for portable equipments such as video cassette recorders, lap-top type computers and portable telephones owing to their high energy density and reliability. These batteries have a metal casing of cylindrical or rectangular shape, a capacity of about 0.5 Ah to 3 Ah, and are configured of cells to make up a small-sized sealed alkaline storage battery. In practical applications, several to several tens of cells are generally contained in a synthetic resin casing or tube.
These small-sized sealed alkaline storage batteries have a battery capacity as small as about 0.5 Ah to 3 Ah, and therefore generate only a small amount of heat per cell at the time of charging or discharging. As a result, in the case where they are used in a resin casing or tube, an appropriate balance or equilibrium is maintained between heat generation and heat discharge. Therefore no significant problem has been posed with regard to a temperature increase of the battery. Also, although the electrodes of the alkaline storage battery expand as a result of repetitive charging and discharging, no serious problem of casing deformation due to electrode expansion has been posed in view of the fact that the casing is made of a cylindrical metal. This is also true with the rectangular type of battery, for which no special configuration has been necessary for the casing.
Nevertheless, there is an ever-increasing demand for medium and large-sized batteries (the medium-sized battery is defined as those from 10 Ah to 100 Ah in capacity, and the large-sized one as those 100 Ah or more in capacity. The number of cells used is several to several hundreds for either type) high in energy density as a mobile power supply for various devices including home-use appliances and electric vehicles. The open-type nickel-cadmium storage battery and the lead-acid storage battery are used for energy storage and as a power source in case of power outage. In spite of these advantages, these batteries have the disadvantage of the need of troublesome maintenance such as for filling an electrolyte solution during the lifetime. In view of this, there has been a demand for a battery suitable for a mobile power source for various applications including home-use appliances and electric vehicles, which is free of maintenance, by having a sealed configuration.
As explained above, in the case where an alkaline storage battery is used as a mobile power supply for various devices including home-use appliances and electric vehicles, the battery is required to be sealed and increased in size to medium or large scale at the same time. More specifically, it is necessary to connect a multiplicity of the cells in series while sealing them in order to increase the electric capacity and voltage of a unit.
The battery generates Joule's heat and reaction heat due to electrode reaction at charging and discharging operations. The cells, with an increased electric capacity and sealed configuration, increase in the amount of heat accumulation, with the result that heat dissipation out of the battery is retarded and the generated heat is accumulated within the battery. Consequently, the internal temperature of such a battery rises by a degree more than that of a smaller battery. A module battery including a series of cells having such a large capacity or a pack battery including a series of module batteries is configured of several tens to several hundreds of cells arranged contiguously to each other.
In order to obviate the above-mentioned problems, a heat dissipation device for the storage battery system has been suggested by Japanese Laid-Open Patent Publication No. Hei 3-291867 configured of a multiplicity of cells generating heat at the time of charging, in which each cell includes positive electrodes, negative electrodes and an electrolyte, and in which a space for allowing air flow is formed between the cells with a ratio of space width to cell width set to a range of 0.1 to 1.0.
The above-mentioned configuration of forming a space for air flow between cells with the ratio between the space width and cell width set to 0.1 to 1.0 still poses the following problems:
(1) Because of the fact that the electrode group expands with repetitions of charging and discharging and an increased internal pressure of the battery, the casing expands thereby making it difficult to maintain a constant space width for allowing air flow. In order to maintain a constant air space between cells, the casing strength must be increased. The increase of the casing strength requires an increased thickness at the expense of an increased casing weight or volume, battery weight or volume and hence a decrease of energy density. PA1 (2) In the case where the casing expands and is deformed due to an increased internal pressure of the battery, there occurs a space between the electrode group and the casing. With the space formed between the electrode group and the casing, the rate of heat transmitted to the casing against the heat generated by the electrode group is extremely reduced. As a result, it is desirable to keep the casing in contact with the electrode group. PA1 (3) For applications to a mobile power supply, a configuration of a module battery having about 5 to 40 cells or a pack battery which includes two or more module batteries and is equivalent to about 10 to 300 cells is required to reduce the variations in battery performance such as battery capacity and improve the battery performance such as energy density and the mechanical strength for preventing displacement due to vibrations.
An object of the present invention is to solve the above-mentioned problems and provide a battery in which the reduction in energy density and deformation or breakage of the casing of the module or pack battery are prevented and the mechanical strength of the module or pack battery against vibrations is improved.
Another object of the present invention is to provide a battery which is free of deformation or breakage of the casing or displacement of the unit or pack battery after repetitive charging and discharging or long time operation, and which can efficiently dissipate the heat generated in the battery at the time of charging and discharging out of the battery system, thereby leading to a superior constant battery performance.